1. Field of the Invention
The present invention relates to a vehicular use power distribution apparatus which feeds power for various electrical components, apparatuses, and equipment mounted in a passenger car or other vehicle, more particularly relates to a vehicular use power distribution apparatus and a vehicular use power source apparatus with which a reduction of power consumption is achieved.
2. Description of the Related Art
When a passenger car or other vehicle is stopped or is not being operating, while the vehicle may be designed to sound an alarm to indicate when, for example, the door is left half open, the driver will sometimes not notice the alarm and leave the door open for a long time--resulting in exhaustion of the battery life.
Further, if the driver mistakenly leaves the headlights or room light on when the vehicle is not being operated, the battery will also be drained.
There are various other factors which will drain the battery power when a vehicle is not in operation. A typical example is the supply of power for the electronic control system--which has to be kept in fast starting state at all time in order to start up the vehicle. At the heart of the electronic control system is an electronic control unit which is normally constituted by a microprocessor etc. To minimize the power consumption of the microprocessor etc., they are often placed in a sleep mode when the vehicle is not in operation or stopped. Even in the sleep mode, however, if there are a large number of microprocessor-based electronic control units, a considerable amount of power will still be consumed.
Further, when leaving a vehicle idle for a long period of time, such as when placing a vehicle in long term storage or when shipping a vehicle overseas and transporting it over the long period of time from the country of origin to the destination country, the buildup of a leakage current in the sleep mode causes the battery life to drop considerably or exhausts the battery life.
In particular, in recent years, vehicles have made increasing use of electronics. Numerous electronic apparatuses are now being mounted in vehicles. This is further increasing the consumption of the battery. There are limits to a battery's capacity, however, so the problems described above cannot be sufficiently solved.
To prolong the battery life, various approaches for reducing the consumption of battery power may be considered.
For example, to deal with the above-mentioned failure to turn off the room light, the method may be considered of having the vehicle monitor the situation and automatically stopping the supply of power to the inadvertently left on room light and all other electrical systems which should not be operating when the vehicle is not in operation or stopped after a predetermined time has passed after the vehicle stops being operated or has been stopped. However, the electronic control system for monitoring the status of the vehicle has to continuously operate, so the supply of power for the electronic control system consumes the battery power as a leakage current. Even when the electronic control system is in the sleep mode, if there are a large number of electronic control circuits and the vehicle is not operated over a long period of time, a considerable amount of the battery power will be consumed.
When a vehicle is put away for long term storage, shipped overseas, or otherwise not used for a long period of time, the fuse at the output side of the battery is sometimes removed. It is true that by removing the fuse, the supply of power to all of the electrical systems of the vehicle is completely stopped, so the only reduction in the battery power will be that accompanying long term natural discharge.
However, removing a fuse when not using a vehicle for a long term and reinserting it when again using the vehicle is troublesome. Also, the worker might touch the power line of the battery so the work of detaching and attaching the fuse is dangerous.
Conventional power supply systems are not clearly divided into a power supply systems for loads such as room lights and headlights and power supply systems for electronic control systems. Therefore, the above measures to reduce power consumption when the vehicle is stopped are not effective.
Further, in passenger cars and other vehicles, the electronic control circuit, electrical components, power windows and wipers, and other auxiliary equipment are normally supplied with power from a battery, relay box, and joint box via power feed lines (cables). The auxiliary equipment is arranged at predetermined locations in a vehicle. For example, the meters etc. are arranged at the instrument panel, while the hazard lamps are located at the rear of the vehicle.
Generally in the engine compartment of a vehicle, the relay box is located far away from the battery. The battery and the relay box are connected by a thick large current carrying cable. Normally, the battery and cable are connected by engaging a taper terminal defined by JIS D5301 and an adapter crimping the cable to a nut-and-bolt terminal and then tightening the two by the nut and bolt.
It is however troublesome space-wise and design-wise to lay a thick large current carrying cable between the battery and relay box in the engine compartment and to lay cables to the load side. Further, since the battery and relay box each take up space, the two occupy a certain amount of space in the engine compartment and make the engine compartment cramper.
In particular, the increasingly sophisticated functions of vehicles mean that various members, apparatus, and electronic control apparatuses are located in the engine compartment. The power cables therefore have to be weaved between these apparatuses and members and become much more complicated.
When for example a short-circuit occurs in a power feed line, the vehicle is involved in a collision, or some other problem or trouble occurs in the vehicle, the supply of power to the electrical components, electronic control apparatuses, etc. should be stopped quickly.
It has been proposed to shut off the power source when a vehicle is involved in a collision, but the conventional method has been to break the circuit in the relay box, so the large current carrying cable between the battery and the relay box continues to be live. Accordingly, there is a possibility of the live cable in the engine compartment will short-circuit and another accident will be caused.
Further, while the battery terminal, as described above, is prescribed in JIS D5301, the plus pole and minus pole of the nut-and-bolt terminal are the same in shape, so there is a possibility of connection with the wrong polarity. If connected in reverse, the electronic apparatuses and electronic devices mounted in the vehicle may be ruined.
In another area, normally, one battery or two batteries connected in parallel are mounted in a vehicle. The battery is a storage battery comprised of a plurality of cells each having an electromotive force of approximately 2.1V per cell connected in series and supplies 12V or 24V of voltage for driving loads from the cells at the two ends. This voltage is used for starting the engine and driving other loads of the vehicle. The output terminal of the vehicular storage battery is connected to the mounted load apparatus and starter via a relay box or joint box.
As already mentioned, large numbers of electronic control circuits have been mounted in load apparatuses along with the increasing sophistication of vehicles. 5V to 6V is need to drive these electronic control circuits, so the voltage supplied from the battery cannot be used as it is. Conventionally, therefore, for example, each mounted load apparatus is provided with a DC voltage transformer for transforming the 12V or 24V voltage from the battery for driving load apparatuses to the 5V to 6V for driving the electronic circuits.
However, if each mounted load apparatus is provided with an expensive DC voltage transformer, the number of DC voltage transformers will increase along with an increase in the number of mounted load apparatuses, the hardware configuration will become more complicated, and the manufacturing cost will increase. Note that the further use of electronics in vehicles will result in an increase in the number of load apparatuses mounted as well.
To solve these problems, it has been proposed to provide one DC voltage transformer in the relay box, transform the voltage for driving loads supplied from the battery to a voltage for driving electronic circuits all together in the relay box, and distribute the obtained voltage for driving electronic circuits to a plurality of electronic control circuits.
According to this method, it is possible to reduce the number of the DC voltage transformers, however, at least one DC voltage transformer is still needed. In this case, a large capacity DC voltage transformer is needed, so the price becomes very high.